Known to the prior art is an electron beam accelerator (cf. U.S. Pat. No. 3,433,947 published in 1969), comprising a completely shielded vacuum chamber with an electron beam scanning system, and an exit window made of foil, passing the electron beam into the atmosphere. The material to be irradiated by the electron beam is moved in front of the exit window. To create and maintain the required vacuum in the vacuum volume of the accelerator, a vacuum pump is connected to the vacuum chamber by a pipeline. The pipeline is passed through a hole in the wall of the vacuum chamber. Mounted in front of this hole is a lead plate 1 inch thick to create multiple reflections and, consequently, to attenuate X-ray radiation. This attenuation results from electron deceleration in the irradiated material and when passing through the vacuum volume of the chamber, the pipeline and the vacuum pump into the atmosphere.
Owing to the lead plate the inner part of the pipeline takes a bent configuration and thus its length and resistance increases, which results in a decrease of evacuation rate and in a reduction of a highest attained vacuum in the vacuum chamber. This degradation of vacuum lowers reliability of the electron accelerator on one hand due to shortened service life of the electron source, i.e. electron gun of the accelerating tube, and on the other hand, due to a gas current and an additional decelerating X-ray radiation, thus increasing the probability of an electric breakdown of the tube.
Also known in the art is an electron beam accelerator described in an article titled "Promyshlennye Uskoriteli Serii `Electron` dlya Radiatsionnoi khimii" by V. V. Akulov et al., preprint by NIIEFA, Leningrad, 1974, p. 11. This accelerator comprises a radiation protection metal chamber, accommodating a vacuum chamber with an exit window, an electron beam scanning system, vacuum pumps and a vacuum monitoring device. Since the vacuum pumps and the said device are arranged within the radiation protection chamber together with the vacuum chamber, the pumps are connected to the chamber with straight pipelines (i.e. with no elbows) featuring lower resistance as compared to a bent pipeline used in an electron beam accelerator according to the aforesaid U.S. Patent. Thus, the vacuum pumps can provide higher vacuum in the chamber without any undesired effects associated with degradation of vacuum in the accelerator.
When the accelerator operates, the electron beam, passing through the window of the vacuum chamber not only causes deceleration of the X-ray radiation as it strikes the irradiated material and the elements of the conveyor moving this material under the window but also disintegrates the gaseous medium in the irradiation zone i.e. nitrogen oxygen and carbon dioxide of the air, and forms carbon monoxide, nitrogen dioxide, cyanogen and other active chemical substances. Poisonous, fire--and explosion--hazard substances may also be formed due to the action of the electron beam on the irradiated material and surrounding objects. Since all mentioned elements of the accelerator are enclosed together with the exit window and the irradiation zone within the volume of the radiation protection chamber the above-mentioned substances with high chemical activity and strong X-ray radiation formed in the immediate vicinity to the exit window cause corrosion and destruction of the accelerator elements in the radiation protection chamber.
Thus, reliability of this accelerator, as well as reliability of the accelerator according to U.S. Pat. No. 3,433,947 turns out to be unsufficient, although due to other reasons. Moreover, to prevent leakage of the X-ray radiation outside, all lead-ins of different communications (electric power supply, initial vacuum pipeline etc.) to the elements of the accelerator should have complicated labirinth seal in the radiation protection chamber, which present difficulties in maintenance of the accelerator elements located in the said chamber and of the accelerator as a whole.